The present invention refers to a mechanism for the production of a wrapped yarn which consists of a bundle of spun fibers wrapped round by a binding thread, having a hollow spindle supported between a pair of delivery rolls and a pair of draw-off rolls, a rotating binding-thread bobbin arranged coaxially with the hollow spindle and a housing surrounding the binding-thread bobbin.
A mechanism of the above-mentioned kind for the production of a wrapped yarn is known, in which the housing acting as a balloon-restricter turns at the same angular velocity as the binding-thread bobbin (West German A/S No. 2.428.483=U.S. Pat. No. 4,018,042). The binding thread, here a filament, is wound round the core of a flanged bobbin which prevents the layers of thread from slipping down off the wound body and to that extent is particularly advantageous. Through the rotation of the binding-thread bobbin arranged on the driven hollow spindle and connected fixedly in rotation to it, the bundle of spun fibers delivered by the pair of delivery rolls into the hollow spindle gets wrapped round by the binding-thread and subsequently the finished wrapped yarn is drawn down out of the hollow spindle by the draw-off rolls. Upon drawing the binding-thread off the rotating flanged bobbin which is effected with the formation of a thread balloon, a thread tension is generated so that the binding-thread is wound round the bundle of spun fibers under tension and makes it firm. The thread tension of the binding-thread which depends for its average value upon the speed of rotation of the bobbin body and the fineness of the binding-thread and alters in dependence upon the shape and size of the binding-thread bobbin, influences the yarn structure and according to the known proposal must not be too high.
In continuous operation it has proved disadvantageous that after leaving the pair of delivery rolls fibers detach themselves from the bundle of spun fibers. These as well as other fluff usual in spinning mills can arrive in the region of the rotating binding-thread, get caught by it and accumulate on it. Especially in the case of smooth binding threads the fibers loop themselves round it and get held on the thread balloon by the high centrifugal force between the point of wrap and the greatest diameter of the balloon, where finally a fiber beard forms. In that case the binding thread slides at its draw-off speed through the fiber beard without pulling it with it. Because of the increased centrifugal force as well as the increased air resistance through the fiber beard an increase in the binding-thread tension occurs. A further increase in the binding-thread tension is caused when the fiber beard the binding-thread balloon collapses and hence rubs against the bobbin with the binding-thread. Such an increase in the thread tension in the binding-thread is undesirable since as mentioned above it influences the yarn structure and also the technological characteristics of the yarn, in particular the ultimate strength and thereby has a disadvantageous effect upon the yarn quality.
Under certain circumstances through the formation of the fiber beard it may even come to yarn breakage and hence to an interruption of the spinning process. The escape of the fibers from the fiber formation cannot be completely prevented if a false twist is imparted to the bundle of spun fibers before the entry into the hollow spindle.
Besides these technological disadvantages the increased consumption of energy of the housing running round with the binding-thread bobbin has proved disadvantageous.
The object of the present invention is to avoid these disadvantages and to create a mechanism which enables the production of a wrapped yarn satisfactory in quality while at the same time reducing consumption of energy.